I assume you are getting no console response?
I'd first start with making sure that the DRAM (if you have any extra aside from the 16MB on board) and the flash are seated properly...and also any WIC/VIC cards. If that's no help then maybe swapping DRAM would help. Although I'd assume you'd get some console output even if the dram were bad. If you are getting no console output at all, then you are probably talking about a bad router, boot rom, and/or power supply.